This invention relates to variable impedance dependent (load pull or source pull) testing of microwave power transistors using automatic microwave tuners in order to synthesize reflection factors (or impedances) at the input and output of said transistors at the fundamental and various harmonic frequencies.
Modern design of high power microwave amplifiers, oscillators and other active components, used in various communication systems, requires accurate knowledge of the active device's (microwave transistor's) characteristics. In such circuits, it is insufficient and inaccurate for the transistors operating at high power in their highly non-linear regions and close to saturation, to be described using analytical or numerical models only. Instead the devices must be characterized using specialized test setups under the actual operating conditions.
A popular method for testing and characterizing such microwave components (transistors) for high power operation is “load pull” and “source pull”. Load pull or source pull are measurement techniques employing microwave tuners (2, 4) and other microwave test equipment (1, 5). The microwave tuners in particular are used in order to manipulate the microwave impedance conditions under which the Device Under Test (DUT, or transistor) is tested (3) [1] (FIG. 1).
A system control computer (9) is needed to communicate (6) with the instruments (5) and the tuners (7, 8). The control computer directs the tuner motors (12, 12a, FIG. 2) and reads data from the instruments, both during the tuner calibration and during the DUT measurement.
When the DUT's are driven into saturation, which is a typical amplifiers operation for highly efficient amplifiers, then they operate in a highly nonlinear range, distort the source signal and create energy at the harmonic frequencies. The appropriate impedance tuner for this operation is a device that is able to create user-defined impedances at the fundamental (Fo) and harmonic frequencies (2Fo, 3Fo, 4Fo . . . ). A tuner allowing a three frequency impedance synthesis and associated calibration and tuning software are integrated into a multi-frequency impedance synthesizer, as described in [4]. For several applications, however, wideband tuners are used, which allow control of the impedance only at the fundamental frequency (Fo), [1, 2].